What does HER2-low mean on a breast cancer report?

Immunohistochemistry (IHC) shows HER2 protein staining on the surface of tumour cells. In situ hybridisation (ISH) checks for extra copies of the HER2 gene. If your report says IHC 2+, look for the ISH result from the same sample. It determines how the 2+ score is classified. [1]

If an older report says only “HER2-negative,” the original IHC score can still help. The China Anti-Cancer Association classifies IHC 1+ and IHC 2+ without ISH amplification as HER2-low. In recurrent or metastatic disease, the distinction can affect which antibody-drug conjugates are worth discussing. The score by itself does not determine whether to use a medicine. [1]

Bring the original pathology report, HER2 IHC result, any supplementary ISH report and a list of treatments you have had. If you need to borrow slides, ask the receiving hospital which stained slides, unstained slides or paraffin blocks it needs. Follow the original hospital’s procedures to obtain them. Beijing Tsinghua Changgung Hospital advises checking that the pathology number on the report matches the slides. The breast oncology team assesses treatment options, and the pathology team reviews tissue and test results. [1][2]

Will I need another biopsy if my old breast cancer report only says HER2-negative?

Find the original IHC score and check which samples are still kept. Your clinician and pathology team will decide whether they can review existing tissue or need a new sample. [1][2]